Osteosarcoma

Osteosarcoma is a malignant bone cancer; together with Ewing's sarcoma it accounts for most primary bone malignancies. There is a preference for the metaphyseal region of tubular long bones. 50% of cases occur around the knee. It is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone.

Pathology

The tumor may be localized at the metaphyseal end of the long bones. Most often it affects the upper end of tibia or humerus, of lower end of femurus. The tumor is solid, hard, irregular ("fir-tree" or "sun-burst" appearance on X-ray examination) due to the tumor spicules of calcified bone radiating in right angles. Surrounding tissues are infiltrated.

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Microscopically: Tumor cells are very pleomorphic (anaplastic), some are giant, numerous atypical mitoses. These cells produce osteoid describing irregular trabeculae (amorphous, eosinophilic/pink) with or without central calcification (hematoxylinophilic/blue, granular) - tumor bone. Tumor cells are included in the osteoid matrix. Cartilage may be present. Presence of immature blood vessels (sarcomatous vessels lacking endothelial cells) favors the bloodstream metastasizing. 1

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